Hyaluronan is an anionic, nonsulfated glycosaminoglycan distributed throughout connective, epithelial, and neural tissues. Hyaluronan is a polysaccharide built of disaccharide repeating residues of -3)-N-acetyl-β-D-glucose amine-(1-4)-β-D-glucuronic acid-(1-., provided as a sodium salt:
It is a very large molecule and can have a molecular weight of several or more million Daltons. Hyaluronan is present in most tissues in mammals in the extracellular matrix. In mammals, hyaluronan is found in higher amounts in the umbilical cord, and it is a constituent of the vitreous body and joint cartilage. Hyaluronan is an important constituent of the synovial fluid. It has high viscosity and provides lubrication to the joints.
Hyaluronan and modified derivatives of hyaluronan are currently used in in vivo applications such as eye surgery, cosmetic injections and intraarticular injections to treat osteoarthritis.
Osteoarthritis is a degenerative joint disease and a very common condition. Knee joints, hip joints and shoulder joints are often affected, and symptoms can be disabling to different degrees. A common treatment is oral intake of non-steroidal anti-inflammatory drugs (NSAIDs). Some of these NSAIDs are known to give gastrointestinal problems after extended use and such intestinal complications are far from uncommon. In osteoarthritis, local administration of the drug, e.g. by injection, would be desirable, but the duration of a small NSAID molecule is relatively short and a more prolonged duration is necessary for efficient treatment.
Many studies have been performed to investigate the efficiency of hyaluronan in arthritis treatment, see Lohmander et al (1996) [1], but the results of various studies have been contradictory and lately some reports indicate that injection of hyaluronan is not efficient, see Jorgensen et al [2] and Arrich et al [3]. In spite of this, several hyaluronan products for treatment of osteoarthritis are currently in use.
In the ophthalmic area, cataract surgery is quite common and typically steroid-containing eye-drops are used post-surgery to suppress inflammation. The patients are often elderly and sometimes have difficulties taking the eye drops as prescribed. A slow release composition that could be left in the eye could alleviate the use of such inflammation suppressing eye-drops.
There has been a considerable interest in controlled release systems for the distribution of active pharmaceuticals over an extended time period, and hyaluronan has been used both in mixtures with drugs and in systems where a drug is attached to the hyaluronan molecule, for example, with a covalent bond, usually with an ester or amide group, directly or through a spacer molecule.
EP1710257 A1 discloses a drug bound with an ester linkage to a spacer which in turn is linked through an amide bond to hyaluronan. The drug is released by cleavage of the ester bond, leaving the amide residue on the hyaluronan polymer. An amine is first made at position C-6 of the GlcNAc moiety and then coupling is made through an amide linkage through to hyaluronan.
WO 96/35720 and WO 96/35721 disclose succinyl hemi-ester derivatives of drugs. In WO 96/35721, the derivatives are synthesized by a method wherein, inter alia, the carboxyl group of the hemi-ester is converted to a reactive acid chloride using oxalyl chloride, and the drug-hemi-ester-chloride is subsequently reacted with hyaluronan in DMF and an excess of pyridine to obtain an ester bond to hyaluronan or hyaluronan benzyl ester. Because succinic hemiesters are made of pharmaceutically active compounds, and then acid chlorides are made from the drug-hemiesters, the pharmaceutically active compound must not be susceptible to chlorination at other positions. The derivatized drugs are then reacted with hyaluronan in an aprotic solvent. In order to dissolve hyaluronan in an aprotic solvent, the hyaluronan must be modified to a hydrophobic salt such as tetraalkyl ammonium or tetraalkyl phosphonium, or to make some other hydrophobic derivative, for example, esters. WO 96/35721 references Kyyronen et al [7], where the release of methylprednisolone from microspheres and films made of ethyl esters or benzyl esters of hyaluronan and of the methylprednisolone ester linked to hyaluronan was studied in vitro and in vivo. In the in vivo model, the ocular bioavailability was studied by measuring the drug released into tear fluid. Hemi-succinate esters of hyaluronan are described in WO 96/35720 with the purpose to make various heavy metal salts of the polymer.
WO 2009/074678 describes the coupling of camptothecin to hyaluronan via a linker. The procedure involves the synthesis of camptothecin hemi-succinate, followed by the activation of the carboxyl of the hemi-succinate to the n-hydroxy succinimide ester, which in turn is reacted with the tetrabutylammonium salt of hyaluronan in dimethyl sulfoxide. Also a camptothecin-(aminoacid or peptide)-NH—CO—CH2—CH2—CO-hyaluronan derivative is described. The procedure is similar to that used in WO 96/35721, and requires that a hydrophobic salt of hyaluronan is made before the coupling reaction to hyaluronan.
In the described publications, a hemi succinate ester of the drug is made first and then reacted with hyaluronan. Easier methods for production of hyaluronan conjugates are desired, as are hyaluronan conjugates having improved properties.